Flying wing with pitch control canard?

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Jeremy Harris, Jan 11, 2007.

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  1. Jan 17, 2007 #21

    Jeremy

    Jeremy

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    Very many thanks yet again for the useful advice and tips. I was really impressed with your draughtsmanship, Topaz and really like your design. Mine is pretty similar, except for being a plank type wing and only having one seat. The rough sketch below shows the non-tapered wing version.

    Normam, thanks for the links, I had made a start on scribbling hand written notes by the formulae on my copy a few months ago, but ran short of patience half way through the exercise! I really must get back and finish the job. Thanks also for the link to Koen's new site. I had a bookmark to the old one and hadn't realised that it had moved. I like the way his mind works, much like mine in some ways, I think.

    The foam cores for the model wings should be here at the end of the week, so I'd better get back to finishing the model fuselage. Only one slight error so far. I laid up a scale size carbon fibre landing gear spring. Of course, being scale size it's massively stiff compared with the real one...............

    I'll have to write out a hundred times "remember, mass scales in proportion to the cube of the linear dimensions"............... I don't think this will matter for the model at all, as it'll be a heck of a lot stronger in proportion to it's mass than it needs to be all over.

    Jeremy
     

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  2. Jan 18, 2007 #22

    mogren

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    The canard is the most efficient form or pitch control. The canard controls pitch by lifting the nose, rather than pushing down the tail, increasing total lift. It does look a little funny and some old timers dont think it is right. "Birds have tails, not long noses" Ever seen a Goose??
    Anyway, as you may design this wing. You will need to get a reasonable distance from the vertical tail to the CG. Any design book will give the size VS distance. As you have the straight wing, the fin is very close to the CG . You will need a huge fin to keep the plane straight, or put the fins back on booms. Some guys have solved this issue with tip /drag rudders. These seem to work very well and you should at least look at them, esp with a straight wing. I cant think of any low speed, straight flyingwings that dont have tip rudders for this reason.
    The same with the pitch control. The wing will need to have some reflex in it , this looses lift and makes a bunch of other control /pitch/CG problems. The further the pitch control is from the CG and CP , the less drag is induced by the pitch control, and the more authority the pitching surface has.
    The canard pitch control allows some canard loading. This itself allows the CG to be moved foreward a little, more depending on the canard size. The foreward Cg will give the fins more authority. Rutan is a smart guy. He swept the " Longeasy" to move the tip fins farther back, increasing their effectiveness. The wing looses lift and gains weird stall characteristics this way and the Longeasy gained fences midway out the wing to help, along with a new set of tip fins/plates. Mike Ogren / (tandemwing pusher.)
     
  3. Jan 18, 2007 #23

    Topaz

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    Well, thanks. Comes from being a graphic artist by trade - I can make a very pretty picture of something that may or may not actually be able to fly. ;) The software was Adobe Illustrator, which is good for the 'pretty' part, but not so much for finished, accurate, drawings unless it's just a substitute for good old fashioned pencil, paper, and T-square.

    I like your airplane. With the low aspect ratio, I suspect your gear is going to end up a bit longer to handle the rotation necessary for takeoff and landing, but it's a neat little beast! I'll look forward to hearing about (and seeing pictures of!) your model testing!
     
  4. Jan 18, 2007 #24

    Topaz

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    Oh, possibly, but with the short span the elevons won't develop much adverse yaw moment (relative to a wing of more conventional AR) and the prop will help some, so long as the engine is turning. I'm sure the model testing will show whether the basic characteristics are adequate, even if it's not possible to pull any kind of accurate numbers from that method.

    As with anything, reflex is a compromise. It doesn't cause problems in and of itself. "Control/pitch/CG" issues have to be addressed properly in the design stage no matter what configuration you use. It can be done adequately with a reflexed plank, although it does tend to be more difficult a design effort than a 'conventional' tail, either forward or aft. "Losing lift" is a relative thing as well, and as long as the aircraft meets it's design goals, doesn't necessarily become an issue at all.
     
  5. Jan 18, 2007 #25

    Jeremy Harris

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    Thanks Mike. I'm using a reflexed section. Having spent a couple of days running numbers through both DesignFoil and JavaFoil, I settled on the Fauvel section modified to 12% as being about the best for the range of Re etc. The differences between the various reflexed sections I looked at (probably around a couple of dozen in all) seemed pretty small, but the modified Fauvel had an apparent slight edge in having it's drag bucket centred close to where I expect cruise Cl to be. I've no doubt that with more experimentation I could find a slightly better section but this looks OK to start with. It does have a slightly higher value of Cm0.25 than I think might be optimum for least drag, but at least I can be reasonably sure that I can keep it pitch stable with a more forward C of G.

    The fin area and moment arm should be OK according to my sums, although I think the rudder area needs to be increased. The wing span is relatively short and overall my value for Vv seems consistent with other similar designs that are known to work.


    Topaz,

    I'm the other way around, I can only design stuff with a ruler etc, I can't draw to save my life.

    I agree about the gear position, as shown it can only get to about 7 degrees AoA at rotation, not enough for a slow landing. I solved this last night (UK time, it's just before 08:00 here at the moment), not by making the gear taller, but by shortening the nose gear leg and changing the wing incidence to the fuselage. I now have it set for near zero lift (slightly negative incidence) with the nosewheel on the ground and this gives sufficient rotation to allow the wing to get to about the predicted stall AoA before the tail skid touches. I flew a conventional pusher ultralight for a while that had the wing set at negative incidence on the ground and found it a useful attribute to have. Although it means having to lift the nosewheel as soon as possible on take off (or else you just hurtle along with no sign of ever going up), it does off the advantage of tending to keep the aircraft pinned to the ground as soon as the nosewheel is down, handy with a low wing loading in gusty weather (I guess you've all heard the stories about English weather!).

    I should be getting on with work right now, but I've been thinking about the simplest design of control mixer for the elevons on the drive into work, so might find myself doodling a few ideas for the next hour or so.

    Jeremy
     
    Last edited: Jan 18, 2007
  6. Feb 23, 2008 #26

    Hugh Lorimer

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    Hi Jeremy, we have spoken before, I am in the middle of updating my web site this week end to include photos and Drgs. of a canard and a flying wing on www.hughlorimer.co.uk . Hope to have it completed by Mon.?

    Hughie.
     
  7. Feb 24, 2008 #27

    9aplus

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    One question Hugh

    How far, you are, with Quaich full scale development.
    Flight already or still in preparations?

    Regards

    Djani
     
  8. Feb 24, 2008 #28

    RacerCFIIDave

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    Flying wings....all I've got to say is remember why Edwards AFB is so named...

    Flying wings have a truly nasty tendency to tumble over backwards when stalled...

    You could ask Glen Edwards...except you'd need to hold a seance to do so...


    In Liberty,

    Dave
     
  9. Feb 24, 2008 #29

    Hugh Lorimer

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    I await weather window to fit wings and struts, after that connect the aileron operating rod hinges to operating quadrants, carve a prop and fit the spinner and finally fit seat straps. See www.hughlorimer.co.uk for some photos etc
     
  10. Feb 24, 2008 #30

    Norman

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    It wasn't a tumble, it was a spin during an aft CG stall test. Although the specifics are a bit vague (probably because Northrop didn't like to admit that he still had a lot of development work to do) the fact is that Forbes and Edwards were scheduled to do the aft CG stall series that day. Latter Chuck Tucker attempted to finish those stalls in the remaining YB-49 but with the gear down and 15 degrees of flaps to help prevent over-speeding during recovery. After one spin with the CG at 29 1/2% he announced that the spin tests were complete. Since the people on the ground had just watched (presumably on radar) a 90,000 lb airplane fall 22,000 ft they readily agreed. This CG position is aft of that plane's neutral point so it's not surprising that the plane departed but the altitude loss was apparently a big shock back then. These days everybody knows what will happen if your static margin is to small but the newbies always push it.
     
  11. Feb 25, 2008 #31

    Topaz

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    While it's certainly possible to design a flying wing that will exhibit this behavior, and quite a bit easier to do than for a 'conventional' airplane, such a tendancy is still a result of a badly-done design, and not something that's inherent to the type in general.

    Such myths persist, amongst others. As Norm points out, even the most 'well-known' example of the behavior isn't confirmed or even likely. The YB-49, while having enough taper to make tip stall likely, had very large slots near the tips which would counteract the tendancy - in fact, that's the reason they were there in the first place.
     
    Last edited: Feb 25, 2008
  12. Mar 9, 2008 #32

    Hugh Lorimer

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    I built a 1/4 scale R/C model of my flying wing design and put it through an extensive series of tests. The stall was a non event as far as tests were concerned they were abreviated due to a cow tramping on the model. I did not try rearward GofG. Adjustable lead plates compensate for pilot weight changes. I used large area/very small deflection ailerons. Landing flare was around +10°, no adverse yaw could be detected, `Out only` rudders worked well.
     
  13. Jan 10, 2013 #33

    topspeed100

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    How can one design a wing so that it never comes near a stall at any of its part ???
     
  14. Jan 11, 2013 #34

    deskpilot

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    Digging up posts from 1008! Gee TP, you must be bored. Good question but.
     
  15. Jan 11, 2013 #35

    highspeed

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    Limit the control authority of the elevators/elevons so they can't raise the angle of attack enough to get past the critical angle of attack. Whether this is advisable is another matter entirely.
     
  16. Jan 11, 2013 #36

    topspeed100

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    Not bored just trying to figure out how a canard flies...I am getting there..this is a good site for it.
     
  17. Jan 11, 2013 #37

    topspeed100

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    This previous comment from Orion sorta blew my mind.

    Why can the wing not be allowed to stall..how can you test stall caracteristics etc ?

    Is canard dangerous in stall or what ?
     
  18. Jan 11, 2013 #38

    Jaxx

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    This one..?
    Building the C.P. 150 Onyx: In the beginning ...
     
  19. Jan 11, 2013 #39

    bmcj

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    It's simple if you think about it. In a conventional arrangement, if the wing stalls, the nose drops and speed increases... this is a self correcting condition.

    If the main wing of a canard stalls before the canard does, the tail drops and makes the situation worse. Once in this condition, you will likely lose all forward speed and may even tumble or tailslide. An easy recovery may not be possible. That is why the canard should stall first and prevent the wing from stalling.
     
  20. Jan 12, 2013 #40

    Hugh Lorimer

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    Jeremy, I am about to test my Sgian Dubh by towing behind a car like a glider at a secret site shortly.(in Scotland) might answer some of your questions?

    Hughie.
     

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